Floor drop-in forced circulation electric space heater

ABSTRACT

A fan operated, drop-in floor space heater is provided having a generally rectangular enclosure. A fan is mounted centrally within the enclosure and draws air inwardly along a central portion of a grating forming a top wall for the enclosure. The fan forces cooler intake air over a heating element and against a bottom wall of the enclosure. The bottom wall deflects the heated air upwardly and outwardly along the side portions of the grating. The heater is designed to operate at one of a preselected input voltage, for example, 120 or 240/208 volts, and at varying output wattages within the input voltage ranges. Field selection of heater operating range is provided by a novel wiring system which permits selection of any desired one of the possible multiple voltages and wattages by simple connection changes internally of the heater. All of the active elements of the heater are assembled in a single structural unit which is removable from the enclosure. Unit removal permits the desired wiring change to be made easily.

United States Patent 9 1191 Steiner ELOOR DROP-IN FORCED CIRCULATION ELECTRIC SPACE HEATER [75] Inventor: 1 Robert E. Steiner, Creve Coeur,

[73] Assignee: EmersonElectric Co., St. Louis, Mo.

[22] Filed: Mar. 15, 1973 [21] Appl. No.: 341,399

[52] U.S. Cl 219/370, 126/110 R, 165/122,

219/368, 219/376, 338/295, 338/319 [51] Int. Cl H05b'1/00, F24h 3/04 [58] Field of Search... 219/359-361,

2l9/363372, 374-376, 379-382; 126/110 R, 110 B, 117, 116 B, 103; 165/120, 121, 122, 126 55-57; 338/318-320, 295

OQOQQG OQQQQOQQQQODQQOOOO Mar. 11, 1975 3,449,552 6/1969 Graves 338/319 X Primary Examiner-A. Bartis Attorney, Agent, or FirmPolster and Polster [57] ABSTRACT A fan operated, drop-in floor space heater is provided having a generally rectangular enclosure. A fan is mounted centrally within the enclosure and draws air inwardly along a central portion of a grating forming a top wall for the enclosure. The fan forces cooler intake air over a heating element and against a bottom wall of the enclosure. The bottom wall deflects the heated air upwardly and outwardly along the side portions of the grating. The heater is designed to operate at one of a preselected input voltage, for example, 120 or 240/208 volts, and at varying output wattages within the input voltage ranges. Field selection of heater operating range is provided by a novel wiring system which permits selection of any desired one of the possible multiple voltages and wattages by simple connection changes internally of the heater. All of the active elements of the heater are assembled in a single structural unit which is removable from the enclosure. Unit removal permits the desired wiring change to be made easily.

16 Claims, 7 Drawing Figures PATENTEQHAR 1197s SHLU 1 OF 5 THE PM 05 74 T FIG.6.

THEEMOG TA T FIG.|.

PATENTEUHARI 5 v 1 3.870.860 SHEEI 5 BF 5 m l 1 L ir/reri'llfl liiil+fii FIG. 5.

,1 I FLOOR DROP-IN FORCED CIRCULATION ELECTRIC SPACE HEATER BACKGROUND OF THE INVENTION tion type heaters. Convection heaters merely radiate hot 'air upwardly through the top of the heater enclosure. While convectionheaters work well for their intended purpose, they are undesirable in many uses because the grill or top wall of the enclosure tends to rise to undesirably high temperatures during heater operation. This in turn, can make convection heaters dangerous to the touch.

Forced air heaters also are known in the prior art. Conventionally, forced air heaters include a heating element and a fan mounted within an enclosure. The fan is mounted, toward the bottom of the enclosure and the heating means is placed above it. The fan is directed to force a volume of air over the heating element and out the enclosure top. While these prior art forced fan heaters also function well for their intended purposes, they suffer several major drawbacks. For example, where the depth of the heater enclosure is relatively shallow, it becomes difficult to keep the temperature of the fan environment below acceptable levels for long fan life. In addition, the fan can not be positioned to force air over the entire heating element. When this sit-' uation arises, that portion of the heating element having an insufficient air volume forced across it tends to act like a convection heater, with the result that hot spots occur at the top wall of the enclosure.

The invention disclosed herein eliminates these prior artdeficiencies. By positioning the fan so that it directs a volume of air inwardly towards a bottom wall of the heater enclosure, the heater of this invention is able to draw cool air inwardly along a center portion of a louvered top wall. The relatively cooler air maintains the fan environment within safe operating temperature ranges without the need to resort to special baffles or air deflectors. The cool air is directed over a heating element and against a back wall of the heater enclosure. This thoroughly mixes the air. The back wall also redirects the air volume upwardly and outwardly along the sides of the louvered top wall. Two major advantages are obtained by the construction disclosed hereinafter. First, as indicated, the heated air is thoroughly mixed before exiting the heater through the top wall of the enclosure, which eliminates hot spots along the top wall. This in turn allows the heater to have a higher wattage rating for the same air volume movement. Sec- 0nd, exhausting the air along the two sides of the top I wall allows the outlet air pattern to be fanned, without causing recirculation. The disclosed heater also has a novel wiring system which permits selection of multiple voltages and wattages by simple connection changes.

One of the objects of this invention 'is to provide an improved forced air drop-in floor heater.

Another object of this invention is to provide a forced fan drop-in floor heater having a fanned air pattern output.

Still another object of this invention is to provide a drop-in floor heater having acceptable temperatures at the heater outlet.

Still another object of this invention is to provide a floor heater whose construction provides low ambient temperature conditions for a fan mounted in the heater enclosure.

SUMMARY OF THE INVENTION In accordance with this invention, generally stated, a forced air, drop-in floor heater is provided having a fan mounted along the central portion of a grated or lou vered top wall of a fan enclosure. The fan is positioned so as to direct air downwardly toward a bottom wall of the enclosure and draw air into the heater enclosure along a central portion of the top wall. The heater may be programmed to operate at any one of a number of different input voltage-out-put wattage combinations by selective manipulation of the wiring system interconnecting the various components of the electrical system. The possible connection changes are accomplished easily because of a novel structural combination which enables all active components of the heater structure'to be removed as a unit from the heater enclosure.

Other objects will be apparent to those skilled in the art in light of the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is an explodedview, in perspective, of drop-in floor heater of this invention;

FIG.2 is an assembled view, in perspective, of dropin floor heater of this invention;

FIG. 3 is an enlarged sectional view, partly broken away, taken along the line 3-3of FIG. 2;

FIG. 4 is a sectional view, taken along the line 44 of FIG. 3;

FIG. 5 is a view taken along the line 5-5 of FIG. 3;

FIG. 6 is a diagrammatic view of one illustrative embodiment of a connection diagram for the electrical circuit for the drop-in floor heater shown in FIG. 1; and

FIG. 7 is a diagrammatic view of a second illustrative embodiment of a connection for the electrical circuit for the drop-in floor heater shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, reference numeral 1 indicates an illustrative embodiment of drop-in floor heater of this invention. The heater 1 has an enclosure 2 formed by a first pair of oppositely opposed side walls 3 and 4, a second pair of oppositely opposed side walls 5 and 6, a bottom wall 7 and a top wall 8. The walls 3, 4, 5, and 6, the top 8 and the bottom 7 delimit a chamber 18 therebetween.

Top wall 8 is conventional in that the wall 8 has a lip portion 9, extending inwardly from the perimeter of the top 8, which encloses a louvered portion 10. The lou vered portion 10 of the top 8, in the embodiment illustrated, has a pair of louvers 11, best seen in'FIG. 2, dividing the total area of the louvered portion 10 into a leftward directed louver part 12 and a rightward directed louver part 13. That is, the top 8 is approximately evenly divided into two louvered sections about the center of the substantially rectangular area of the are describedas. individual side members, those skilled in the art' will recognizethat one or more of the sides .or theibottom may be formed integrally and joined to form the silhouette illustrated in FIG. 1. Other enclosure designs are compatible with the broader aspects of this invention; Each of the sides 3 and 4 have a pair of openings 77 in them. A tab 14 is inserted through each of the openings 77. .Tabsl4 are L-shaped .in side elevawhile the other leg is attached to either the side 3orthe v side 4 by any convenient method. Metal rivets or spot welds work well,-for example.

At least one of the sides, which in the embodiment illustrated is the side 3, has an opening '15 hit. The opening 15 acts as an access opening to thechamber 18 for a pair of electrieal wires 16. The wire pair 16 is utilized to connect the heater of this invention to a source of electrical energy, not shown.

It is conventional to construct the heater 1 so that the top 8 is removably mounted to the remainder of the enclosure 2. Toward that end, the side walls 3, 4, 5 and 6 all have an outwardly projecting seat 17 along an upper end of the sidewalls. The seat 17 may be integrally formed with'the side walls or the seatmay be manufactured separately and later attachedto the side walls, if desired. The top wall 8 rests on the seat 17 and is secured thereto by any convenient method. Conventional threaded fasteners work well.

In the embodiment illustrated,-the louvers l2 and 13 extend within the chamber 18 when the top' wall 8 is attached to the seat 17. The top 8 has a rim 19 extending tion. One leg of the L extends into the chamber 18 ment forthe mechanical and electrical components of the heater 1. The structure '21 includes a terminal board area 22, a'rise'rjport ion' 23, atop wall 24 and. a pair of oppositely{opposedbraces 25 extending upwardlyfrom and on opposite sides of the top wall 24. It may-beobserved, in FIG. 4, that the supporting structure 21 extends substantially across thewidth of the enclosure 2. Thestructure 21 is designed so that the top wall 24 will abut that leg oflthe L-shaped tabs 14 that extends into the chamber'18', when the-structure 21 is inserted within the cavity 18. Thereafter, conventional fasteners 26 maybe used to secure the structure 21 to the enclosure 2 by attaching the structure 21 to the tabs 14. Any variety of securing means may be utilized, the fasteners26 being merely illustrative of a wide variety of fasteners available. The top wall 24 of support structure 21 has an opening 34 in it. The opening 34 is tangent to the riser portion 23 of structure 21, so that the opening 34 includes a substantial portion of the top 24, with the exception of the corners of the top 24 which are used to mount the structure 21.to thetabs 14.

A heatingielement bank 27 is mounted to structure 21 alongthe terminal board portion 22. Heating element bank 27is conventional and may comprise any of a variety of electrical resistance heaters. in the embodiment illustrated, the heating element bank 27 includes four heating elements 58, 59, 60 and 61 respectively. Such resistance heaters conventionally have a body portion 28 having a convoluted transfer fin 29attached to the body portion. In the preferred embodiment, the structure 21 is sheet metal, and proper insulation between the structure 21 and the body portion 28 of the individual heating elements is provided along the terminal board portion'22 of structure 21 where required.

Each of the respective ends of the individual heating elements 58, 59, 60 and 61 has a connection means 30 attached to it. The connection means '30 is U-shaped in side elevation, the legs of the U forming the male condownwardly from the lip portion 9, which is used to atta'ch the louvers 11, 12 and 13 to the top 8.'Wh ilea number of attaching methods are available, itis convenient to'narrow the ends ofthe louvers 11, 1'2 and 13 and to insert-those'ends into a plurality of openings 85 formed'in the rim 19.A plurality of cross braces '75 extend lengthwise of the top wall 8, which also are attached to the rim 19 similarly' to the method used for the louvers '1'1, 12 and 13. The cross braces 75 lock the respect'ivelouvers'in-place. The louvers may have slits in them forreceiving portions of the cross braces 75 in a flush joint, as best seen in FIG. 4. A pair of spaced baffles 80 also are attached to the rim 19 and extend downwardly-therefrom. The baffles 80 may assume a variety of configurations. In the embodiment of FIG. 3, they merely are rectangular bodies which extend within necto'r for use with a conventional female quick connect type connector, generally indicated by the numeral 31 in FIG.-3.

The four heating elements 58, 59, 60 and 61 are ar- I ranged parallelwise between the respectivehalfs of the the chamber 18for a'predetermined depth, so as to overlap a'pair'of guards 52 attached to a support structure 21. The distancebetween the baffles 80 define the cool air intake for the heater 1. A screen element 20 is inadvertant entrance of foreign objects within the chamber 18.

"The support structure 21 is contained within the chamber 18. Structure 21 is the main supporting eleterminal board portion 22. Referring now to FIGS. 6 and 7, it may be observed that an end 32 of. the bank of'heating elements 27 is connected in a predetermined electrical configuration. An'end 33 of the heating element bank 27 has a plurality of color coded connection lines or jumper wires associated with it. The use of the terminal board area 22 in the structure 21 enables the heater 1 of this invention to-be used with multiple voltages, at various wattage ratings within each voltage. This is a highlysignificant development in fan forced floor drop-in'heaters as it heretoforehas been conventional to use several .fan models to cover the same voltage and wattage ranges thatthe heater 1 covers with a single model. Discussion of the electric circuit of FIGS. 6 and 7 is contained hereinafter. I

A protector 35 is mounted on the end 33 side of the heating element bank 27. Protector 35 is conventional and merely'opens the electrical circuit under certain predetermined conditions. v A pair of braces, denominated 36 and 37 respectively, extend from and between the terminal board portion 22 of the support element 21. The braces 36 and 37 are the main structural supportsfor a fan motor A baffle system surrounds and protects the motor 38 from direct radiation of the heating element bank 27. This baffle system includes a first side wing baffle 41 and a second side wing baffle 42. The baffles 41 and 42 are similar to one another and give the appearance of a frustum in side elevation, best seen in F IG. 3. Because of this similar construction, only the baffle 41 is described in detail.- Baffle 41 includes a side wall 39. The wall 39 has a turnededge 71 and a turned edge 72 integrally formed with it along each end of the side wall 39. When joined with the baffle 42, the edges 71 and 72 form two additional sides forthe baffle protection system. Baffle 41 also has an outwardly extending bottom flange 43 and an upwardly turned lip 44. The side wall 39, and the edges 71 and 72 serve to protect the motor 38 while the lip '44 functions to direct the heated air away from an electrical trough 45, described hereinafter.

As indicated above, the motor 38 is mounted to the braces 36 and 37 and is supported thereby. Mounting may be made directly to the braces 36 and 37. However, the preferred embodiment of this invention utilizes a bracket 46, from and between the braces 36 and 37 as an aid in mounting the motor 38.

Motor 38 is conventional and includes a stator assembly 47 constructed of laminated magnetic material having an axial bore through it. A rotor assembly 48 is rotatably mounted within the bore of the stator assembly 47 and includes a'shaft 49 mounted for rotation with the rotor assembly 48. The shaft 49 has a fan blade 50 attached to it by a conventional hub and nut combination 51. The fan blade 50 is pitched so that the blade draws air inwardly through the top 8, along the central portion of the louvers, over the motor 38, and against the bottom wall 7 of the enclosure 2. This action is important. First, the fan draws the cooler air from the exterior of the enclosure 2 inwardly over the fan 38. This keeps the operating temperature of the fan 38 within safe operating limits. Second, asthe air strikes the bot tom wall 7, it is directed upwardly and outwardly along the sides of the enclosure 2.

As indicated above, the fan 38 is conventional. Commonly, fans utilized in this type of application have a certain horsepower and voltage rating. lt heretofore has been common to utilize a variety of different heater constructions for each different rating. For example, assuming the heater 1 voltage supply is a 120 volt source of electrical power, a motor rated for 120 volts would be used for the fan motor 38. Likewise, where the input voltage is 240 volts, it is not uncommon for the windings of the motor utilized for the fan motor 38 to be changed in order to accommodate the higher voltages found in the application. Such winding changes generally require alteration of wire size and turn number in the windings of the stator assembly 47. Manufacturers or distributors thus have been required to carry an inventory of differently rated heaters in order to supply normal heater applications. As described in more detail in conjunction with the electrical diagram of this invention, the unique construction disclosed herein enables a single rating fan motor 38 to be installed in the heater 1 of this invention, regardless of the voltage found in the application. That is, by manipulating the connections of the terminal board, the heater can be adapted to 120 or 240 volt ratings with a single fan motor 38. This greatly simplifies production, reduces inventory, and makes field installation more convenient.

A pair of guards 52 are attached along two sides of the support structure 21. Generally, the guards 52 are similar in side elevation to the terminal board 22 and riser 23 portion of the support structure 21. The guards 52 however, extend outwardly from the terminal board 22 and prevent foreign objects from coming into elec-v tr'ical contact with the electrical connections made at the terminal board 22 portion of the structure 21. The guards 52 are attached to the structure 21 by any convenient method. Conventional sheet metal screws 53 work well.

Bracket 46 is a sheet metal member, U-shaped in side elevation. The area between the legs of the U are used to house connection elements'for a plug 54. Plug 54 is conventional and is utilized to connect the motor 38 and heating elements 27 to an external source of electrical power, not shown. Toward that end, plug 54 has a conventional male connection portion 55 which is received by a female connector portion 56 carried by the electrical trough 45.

Trough 45 is a frustum shaped member connected to bottom wall 7 by any convenient method. Conventional sheet metal screws'57 may be used. Other conventional connection techniques are acceptable. For example, a plurality of tabs may be punched in the bottom wall 7 and coined or bent over to attach the trough 45 to the bottom wall 7. Trough 45 primarily is used to provide a heat safe zone for a plurality of electrical conductors 58. The conductors 58 enter the enclosure 2 through the opening 15 in the side wall 3.

Referring now to FIGS. 6 and 7, where the heater 1 of this invention is shown somewhat diagrammatically, it is observed that the individual elements 58, 59, 60 and 61 are placed physically across the terminal board 22 portion of the support structure 21. Specifically, the element 58 is electrically connected between a connection node 104 and a connection node 105; the element 59. is electrically connected between a node 106 and a node 107; the element 60 is electrically connected between a node 97 and a node and the element 61 is electrically connected between a node and a node 101. Like numerals are used in both FIGS. 6 and 7 for like components. It also is evident that the source of electrical energy is connected, via the electrical conductors 58 to the female portion 56 of the plug 54. A line 90 is connected from one of the prongs of the male connection portion 55 of the plug 54 to a terminal 91 of the protector 35. A second terminal 92 of protector 63 is connected, by a line 93, to a thermostat 64. A line 94 is connected between thermostat 64 and the connection node 95.

Both the protector 35 and the thermostat 64 are conventional, and any of a variety of commerciallyavailable devices are compatible with the broader aspects of this invention as embodied in the heater 1. It is convenient to place thermostat 64 along the air stream of the heater so that it properly may sample air temperature. For example, the thermostat 64 may be positioned near the motor 38, inboard of the baffles 41 and 42. Consequently, the thermostat 64 is able to sense the cooler air from the exterior of the enclosure 2 which is drawn inwardly of the enclosure by the fan. Other mounting locations are acceptable and are compatible with the broader concept of this invention. Protector 35 may be mounted in a variety of positions, depending upon the to the node 9s.,12;1mem 61 is connected between the nodes 100 and l01. Aline 102 is connected between the node 97 and the node 100. A line 103 is connected between the nodes 95 and 101. .The element 58 is connected between the nodes 104 and 105, while. the element 59 is connected between the nodes 106 and 107. A line 108 is connected between the nodes '100 and 106. A line 109 is connected between the node 106 and the'node 104. A line 110 is connected between the node 101 andthe node 107. The electrical circuit of H6. 6. is completed by a line 111 connected between the node 107 and the node 105. Although shown on the terminal board end 33, the lines 111, 110 and 103 may be placed on either of the terminal board ends 32 or 33, and may be color coded in commercial embodiments of this invention. Thereafter, various heater ratings may be obtained merely by manipulation of the various lines connected between the individual heating elements.

To provide a heater with a rating of. 1125 watts, drawing 9.5 amperes, the line l1l'is removed from between the nodes 105 and 107. This opensthe circuit electrically between the elements 58 and 59 and leaves the elements 59, 60 and 61 active electrically. Heater Tr ating of, 75 0 watts, drawing 6 .2 amperesis obtained by removing the line 110 between the nodes-101 and 107. In this situation, the elements 60 and'6l are connected in parallel with one another and w-iththe motor 38. For 375 watts, 3-.lamperes, the line 103 is removed from between the nodes 101 and 95. The element 60 is connected inparallel with the motor 38 and is the onlyactive one of the elements 58, 59, 60 and 61. It will beunderstood, by those skilled in theart, that only the particular linedesriribed, sometimes known as a jumper wire, is removed in the above multiple conversions. That is, the lines 111, 110 and 103 are not removed serially. I J

Where heater l is intended for 240 or 208 volt applications, the line 96 is removed from the node 97 and connected to the node 107 The line 110 also is disconnected and removed from between the nodes 101 and 107. This configuration is illustrated in FIG. 7, and when so connected the heater lis rated 1500-1125 watts at 240-208 volts respectively. Basically,two paran resistors groupings comprising the elements 58 and 59, and 60and 61, areconnected in series with one another, and the motor 38 is connected across the elernent'60. Inorder to obtain a 750-562 watt, 240-208 rating, the line l03'and the line 111 both are removed from the heater L After removal of the lines 103 and 111, the elements 59 and 60 areserially connected with one another, the motor 38 again being connected in parallelwith'the element 60. Those skilled in the art will recognize that the various circuits described easily may be sketched by redrawing the circuits of FIGS. 6

. 8 and 7 with the various. lines disconnected as described above for each heater rating;

Commercial embodiments of heater l'utilize heating means containing four elements, having a resistance of 9.6 ohms each. Other resistive elements are compatible with the broader aspects of this invention.

' As thus shown and described, a compact unit adaptable over a wide, variety of voltage and wattage ratings is provided The unique feature of drawing air inwardly by the fan .and forcing it outwardlyafter contact with the bottom wall of the enclosure gives good air mixture,

, a forced air output and reduces hot spots along the top Numerous variations, within the scope of the appended claims, will occur to those skilled in the art in lightof the foregoing description and accompanying drawings. Thus, the size, shape and design of the enclosure 2 may be varied. It is convenient, particularly for new construction.applications, to size the length of the enclosure. 2 so that iteasily fits between the floor joists of the building structure. Floor joists conventionally are spaced 16 inches apart, although this distance may vary. The numberof elements comprising the heating element 27 or their rating may be varied. Likewise, a number of fan motors 38 having different rating sizes may be utilized in conjunction with the heater .1. The design of the fan blade may be varied in'other embodiments of this invention. Such variations are immaterial provided the blade 50 functions to draw air inwardly through the enclosure top wall. Other baffle systems for protecting the motor 38 may be used. These variations are merely illustrative.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

l. A heater comprising:

an'enclosure defining a chamber including first and second pairs of oppositely opposed side walls, a

' bottom wall and a top wall, said top wall comprising a' grated" area having a central portion, a first side portion, and a secondside portion, said first andsaid second side portions being on opposite sides of said central portion, at least one of said oppositely opposed side walls having an opening in it permitting access to said chamber for electrical conducting means;

a member' mounted to said enclosure bottom wall and defining a raceway therewith, said opening in said side wall communicatingwith said raceway, said member forming a protecting shield for said electrical conducting means, said member having at least one opening through it;

a unit removably mounted in said enclosure, said unit including a supporting structure defining a first terminal board area, a second terminal board a-rea spaced from said first terminal board area, a first riser portion extending upwardly from said first terminal'board area, a second riser portion extending upwardly from said second terminal board area, and a surface extending from and between said first and said second riser portions, said surface having an opening in it; I heating means attached to said unit and removable therewith, said heating means being mounted from and between said first and said second terminal board areas and electrically connected thereto; electrical conducting means carried in the raceway defined by said bottom wall and said member;

an electrical plug mounted in said enclosure, said plug including a male connecting part and a female connecting part, one of said male and said female connecting parts being mounted in the opening of said member and electrically connected to said electrical conducting means, and the other of said male and said female parts being attached to said unit and electrically connected to said terminal board areas, said male and said female members being aligned for electrical interconnection upon insertion of said unit in said enclosure; and

. a fan mounted to said unit and removable therewith,

said fan being electrically connected to said terminal board areas, said fan being positioned so as to draw air inwardly through said central portion of said top wall grated area and to direct a volume of air against said bottom wall.

-2. The heater of claim 1 wherein one of said first and said second pairs of oppositely opposed side walls has at least one tab attached to respective ones of said side wall pair, said tabs extending inwardly of said chamber to define a seat for said top wall.

- 3. The heater of claim 2 further characterized by a baffle system attached to said unit, said baffle system including a first and a second baffle, each of said first and said second baffle having a side wall, a flange extending downwardly from said side wall, and a lip extending upwardly from said flange, said baffle system being positionally attached to said unit so as to protect said terminal board areas.

4. The heater of claim 3 wherein said heating means comprises four heating elements.

5. The heater of claim 4 wherein said first electrical terminal board area of said supporting structure includes a first connection point, a second connection point, a third connection point and a fourth connection point, said second electrical terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one eachof said four heating elements being electrically connected between said connection points one and five, two and six, three and seven and four and eight; said heater being adapted for 120 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of electrical connecting lines, one 'of said pair of connecting lines being electrically connected from said plug to said third connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point, said first terminal board area having a first jumper wire connected between said first and said second connection points, a second jumper wire'connected between said second and said fourth connection points, a third jumper wire connected between said third and said fourth connection points; said second terminal board area having a fourth jumper wire connected between said fifth and said sixth connection points, a fifth jumper wire connected between said sixth and said eighth connection points and a sixth jumper wire connected between said seventh and said eighth connection points.

6. The heater of claim 4 wherein said first terminal board area of said unit includes a first connection point, a second connection point, a third connection point, and a fourth connection point; said second terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, points two and six, points three and seven, and points four and eight; said heater being adapted for 240/208 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of connecting lines, one of said pair of connecting lines being electrically connected from said plug to said sixth connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point; said first terminal board area having a first wire electrically connected between said first and said second connection points, a second wire electrically connected between said second and said fourth connection points, and a third wire electrically connected between said third and said fourth connection points; and said second terminal board area of said supporting structure having a fourth wire electrically connected between said fifth and said sixth connection points, and a fifth wire electrically connected between said seventh and said eighth connection points.

7. A heater comprising: an enclosure defining a chamber including first and second pairs of oppositely opposed sidewalls, a bottom wall, and a top wall, said top wall having a plurality of louvers in it for permitting passage of air; a protecting member mounted to said bottom wall,

said protecting member and said bottom wall defining a raceway for carrying and protecting electrical conductors, said protecting member having at least one opening in it;

a supporting structural unit removably mounted within said chamber, said unit including a first electrical terminal board area, said first electrical terminal board area comprising a structure for attaching a first end ofa heating means to said supporting structural unit, and a plurality ofelectrical terminal connection points for permitting the completion of electrical connections to said heating means; a second electrical terminal board area spaced from said first electrical terminal board area, said second electrical terminal board area comprising a structure for attaching a second end of a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means;

heating means including a plurality of heating elements attached to said supporting structural unit, each of said heating elements having a first end and a second end, said heating elements being attached to the terminal board areas of said supporting structural unit-along said first and said second ends, the attachment of said heating means to said terminal board areas enabling said heating means to be removed from said chamber with said supporting structural unit, said first and said second ends of said heating element being electrically connected 1 1' I to predetermined-ones of said electrical terminal connection points; I electrical conducting means carried by said enclosure along said raceway; t electrical connection means in said chamber, said connection means including a first part and a second part electricallyinterconnected with .one anothenone of said, first and said second parts being mounted in the opening of saidprotecting member andele'ctrically connected to said electrical conducting means, and the other of said first and said second parts being attached to said supporting structuralunit and electrically connected to at least one of said terminal board areas, said first andsaid secondparts being aligned so as to interconnect electrically upon insertion of said supporting structural unit in said enclosure; a fan mounted to said supporting structural unit, said fan being removable with said supporting structural l unit and being electrically connected to the electri-. cal terminalconnection points; of at least-one of said terminal board areas; and r v means for manually varying the rating of said heater electrically connected to said heating means along said terminal board areas, said rating varying means comprising a plurality of jumper wires connected to. preselected ones of said electrical terminal connection points, individual ones of said jumper wire plurality being rearranged manually to provide rating variation for said heater. 8. The heater of claim 7 wherein said heating means comprises four heating elements, and said electrical connection means comprises a plug having a first male part and a second female part, one of said male and said female partsbeing mounted in the opening of said protecting member, and electrically connected to said electrical conducting. means, and the other said male and said femaleparts being attached to said supporting Structural ,unit and electrically connected to said terminalboard areas. r ,9, Theheater of claim 8 wherein saidfirst electrical terminal. board area of said supporting structure includes a first connection point, a second connection point, a third connection point and a fourth connection point, said second electrical terminal-board areaof said supportingstructure includesa fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements beingelectrically connectedbetween said connection points one and five, two and six, three and seven, and four and eight; said heater being adapted for 120 volt operation, said fan being further characterizedby an electrical motor mounted to said unit having a fan blade mechanically connected toit, said moto rlbeing electrically connected between said thirdand said seventh connection points, said plug including a pair of electrical connecting lines, one of said pair of connecting lines beingelectrically connected from said plug to saidthird connection point, and the other of saidpair of connecting lines being electrically connected fromsaid plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removablyconnected along said first and said second terminal .board areas for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first jumper wire connected between said first and said second connection points, a second jumper wire connected between said'second and said fourth connection points, athird jumper wire connected between said third and said fourth connection points; said second, terminalboard area having a fourth jumper wire connected between said fifth and said sixth connection points, a fifth jumper wireconnected between said sixth andsaid eighth connection points and a sixth jumper wire connected between saidseventh and said eighth connection points.

; 10; The heater of claim 8 wherein said firstterminal board area of said unit includes a first connection point, a second'connection point, a third connection point, and a fourth'con'nection point; and said second terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, points two and six, points three and seven, and points four and'eight; said heater being adapted for240/208 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and saidseventh connection points, said plug including apair of connecting lines, one of said pair of connecting lines being electrically connected from said plug to said sixth connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removably connected along said first and said second terminal board area for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first wire electrically connected between said first and said secondconnection points, a second wire electrically connected between said second and said fourth connection points, and a third wire electrically connected between said third'and'said fourth connection points; and said second terminal board area of said supporting structure having a fourth wire electrically connected between said fifth and said sixth connection points, and ,a fifth wireelectrically connected between said seventh and said eighth connection points.

11. A heater comprising:

an enclosure defining a chamber including a bottom wall, a top wall, and at least one sidewall, said top wall being pervious to air flow to and from said chamber, said sidewall having at least one opening in it;

a protecting member mounted to said enclosure bottom wall andydefining a raceway therewith, said opening in said sidewall communicating with said raceway;

a supporting structural unit removably mounted within saidchamber, said unit including a first electrical terminal board area, said first electrical terminal board area comprising a structure for attaching a first endof a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means; a second terminal board area spaced from said first electrical terminal board area, said second electrical terminal board area comprising a structure for attaching a second end of a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means; I

heating means including a plurality of heating elements attached to said supporting structural unit, each of said heating elements having a first end and a second end, said heating elements being attached to the terminal board areas of said supporting structural unit along said first and said second ends, the attachment ofsaidheating means to said terminal board areas enabling said heating means to be removed from said chamber with said supporting structural unit, said first and said second ends of said heating elements being electrically connected to predetermined ones of said electrical terminal connection points;

electrical conducting means in said enclosure and at least partially carried by said raceway, said electrical conducting means including means for electrically connecting said first and said second terminal board area to a source of electrical power; and means formanually varying the rating of said heater for a given input voltage electrically connected to said heating means along said terminal board area,

said rating varying means comprising a plurality of jumper wires connected to preselected ones of said electrical terminal connection points, individual ones of said jumper wire plurality being rearranged manually to provide rating variation for said heater.

12. The heater of claim 11 wherein said protecting member has an opening in it, said heater being further characterized by electrical connection means interposed in said electrical conducting means, said connection means including a first part and a second part electrically interconnectable with one another, one of said first and said second parts being mounted in the opening of said protecting member and electrically connectable to the source of electrical power through said conducting means, and the other of said first and said second parts being attached to said supporting structural unit and electrically connected to said first and second terminal board areas through said conducting means, said first and said second part being aligned for electrical interconnection upon insertion of said supporting structural unit in said enclosure.

13. The heater of claim 12 further characterized by a fan mounted to said supporting structural unit, removable therewith and electrically connected to at least one of said first and said second terminal board areas.

14. The heater of claim 13 wherein said heating means comprises four heating elements and said electrical connecting means comprises a plug having a first male part and a second female part.

15. The heater of claim 14 wherein said first electrical terminal board area of said supporting structure includes a first connection point, a second connection point, a third connection point and a fourth connection point, said second electrical terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, two and six, three and seven, and four and eight; said heater being adapted for volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of electrical connecting lines, one of said pairs of connecting lines being electrically connected from said plug to said third connection point, and the other of said pairs of connecting lines being electrically connected from said plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removably connected along said first and said second terminal board areas for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first jumper wire connected between said first and said second connection points, a second jumper wire connected between said second and said fourth connection points, a third jumper wire connected between said third and said fourth connection points; said second terminal board area having a fourth jumper wire connected between said fifth and said sixth connection points, a fifth jumper wire connected between said sixth and said eighth connection points and a sixth jumper wire connected between said seventh and said eighth connection points.

16. The heater of claim 14 wherein said first terminal board area of said unit includes a first connection point, a second connection point, a third connection point, and a fourth connection point; and said second terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, points two and six, points three and seven and points four and eight; said heater being adapted for 240/208 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of connecting lines, one of said pair of connecting lines being electrically connected from said plug to said sixth connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removably connected along said first and said second terminal board areas for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first wire electrically connected between said first and said second connection points, a second wire electrically connected between said second and said fourth connection points, and a third wire electrically connected between said third and said fourth connection points; and said second terminal board area of said supporting structure having a fourth wire electrically connected between said fifth and said sixth connection points, and a fifth wire electrically connected between said seventh and said eighth connection points. 

1. A heater comprising: an enclosure defining a chamber including first and second pairs of opposItely opposed side walls, a bottom wall and a top wall, said top wall comprising a grated area having a central portion, a first side portion, and a second side portion, said first and said second side portions being on opposite sides of said central portion, at least one of said oppositely opposed side walls having an opening in it permitting access to said chamber for electrical conducting means; a member mounted to said enclosure bottom wall and defining a raceway therewith, said opening in said side wall communicating with said raceway, said member forming a protecting shield for said electrical conducting means, said member having at least one opening through it; a unit removably mounted in said enclosure, said unit including a supporting structure defining a first terminal board area, a second terminal board area spaced from said first terminal board area, a first riser portion extending upwardly from said first terminal board area, a second riser portion extending upwardly from said second terminal board area, and a surface extending from and between said first and said second riser portions, said surface having an opening in it; heating means attached to said unit and removable therewith, said heating means being mounted from and between said first and said second terminal board areas and electrically connected thereto; electrical conducting means carried in the raceway defined by said bottom wall and said member; an electrical plug mounted in said enclosure, said plug including a male connecting part and a female connecting part, one of said male and said female connecting parts being mounted in the opening of said member and electrically connected to said electrical conducting means, and the other of said male and said female parts being attached to said unit and electrically connected to said terminal board areas, said male and said female members being aligned for electrical interconnection upon insertion of said unit in said enclosure; and a fan mounted to said unit and removable therewith, said fan being electrically connected to said terminal board areas, said fan being positioned so as to draw air inwardly through said central portion of said top wall grated area and to direct a volume of air against said bottom wall.
 1. A heater comprising: an enclosure defining a chamber including first and second pairs of opposItely opposed side walls, a bottom wall and a top wall, said top wall comprising a grated area having a central portion, a first side portion, and a second side portion, said first and said second side portions being on opposite sides of said central portion, at least one of said oppositely opposed side walls having an opening in it permitting access to said chamber for electrical conducting means; a member mounted to said enclosure bottom wall and defining a raceway therewith, said opening in said side wall communicating with said raceway, said member forming a protecting shield for said electrical conducting means, said member having at least one opening through it; a unit removably mounted in said enclosure, said unit including a supporting structure defining a first terminal board area, a second terminal board area spaced from said first terminal board area, a first riser portion extending upwardly from said first terminal board area, a second riser portion extending upwardly from said second terminal board area, and a surface extending from and between said first and said second riser portions, said surface having an opening in it; heating means attached to said unit and removable therewith, said heating means being mounted from and between said first and said second terminal board areas and electrically connected thereto; electrical conducting means carried in the raceway defined by said bottom wall and said member; an electrical plug mounted in said enclosure, said plug including a male connecting part and a female connecting part, one of said male and said female connecting parts being mounted in the opening of said member and electrically connected to said electrical conducting means, and the other of said male and said female parts being attached to said unit and electrically connected to said terminal board areas, said male and said female members being aligned for electrical interconnection upon insertion of said unit in said enclosure; and a fan mounted to said unit and removable therewith, said fan being electrically connected to said terminal board areas, said fan being positioned so as to draw air inwardly through said central portion of said top wall grated area and to direct a volume of air against said bottom wall.
 2. The heater of claim 1 wherein one of said first and said second pairs of oppositely opposed side walls has at least one tab attached to respective ones of said side wall pair, said tabs extending inwardly of said chamber to define a seat for said top wall.
 3. The heater of claim 2 further characterized by a baffle system attached to said unit, said baffle system including a first and a second baffle, each of said first and said second baffle having a side wall, a flange extending downwardly from said side wall, and a lip extending upwardly from said flange, said baffle system being positionally attached to said unit so as to protect said terminal board areas.
 4. The heater of claim 3 wherein said heating means comprises four heating elements.
 5. The heater of claim 4 wherein said first electrical terminal board area of said supporting structure includes a first connection point, a second connection point, a third connection point and a fourth connection point, said second electrical terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, two and six, three and seven and four and eight; said heater being adapted for 120 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of electrical connecting lines, one of said pair of connecting lines being electrically connected fRom said plug to said third connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point, said first terminal board area having a first jumper wire connected between said first and said second connection points, a second jumper wire connected between said second and said fourth connection points, a third jumper wire connected between said third and said fourth connection points; said second terminal board area having a fourth jumper wire connected between said fifth and said sixth connection points, a fifth jumper wire connected between said sixth and said eighth connection points and a sixth jumper wire connected between said seventh and said eighth connection points.
 6. The heater of claim 4 wherein said first terminal board area of said unit includes a first connection point, a second connection point, a third connection point, and a fourth connection point; said second terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, points two and six, points three and seven, and points four and eight; said heater being adapted for 240/208 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of connecting lines, one of said pair of connecting lines being electrically connected from said plug to said sixth connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point; said first terminal board area having a first wire electrically connected between said first and said second connection points, a second wire electrically connected between said second and said fourth connection points, and a third wire electrically connected between said third and said fourth connection points; and said second terminal board area of said supporting structure having a fourth wire electrically connected between said fifth and said sixth connection points, and a fifth wire electrically connected between said seventh and said eighth connection points.
 7. A heater comprising: an enclosure defining a chamber including first and second pairs of oppositely opposed sidewalls, a bottom wall, and a top wall, said top wall having a plurality of louvers in it for permitting passage of air; a protecting member mounted to said bottom wall, said protecting member and said bottom wall defining a raceway for carrying and protecting electrical conductors, said protecting member having at least one opening in it; a supporting structural unit removably mounted within said chamber, said unit including a first electrical terminal board area, said first electrical terminal board area comprising a structure for attaching a first end of a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means; a second electrical terminal board area spaced from said first electrical terminal board area, said second electrical terminal board area comprising a structure for attaching a second end of a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means; heating means including a plurality of heating elements attached to said supporting structural unit, each of said heating elements having a first end and a second end, said heating elements being attached to the terminal board areas of said supporting structural unit along said first and said second ends, tHe attachment of said heating means to said terminal board areas enabling said heating means to be removed from said chamber with said supporting structural unit, said first and said second ends of said heating element being electrically connected to predetermined ones of said electrical terminal connection points; electrical conducting means carried by said enclosure along said raceway; electrical connection means in said chamber, said connection means including a first part and a second part electrically interconnected with one another, one of said first and said second parts being mounted in the opening of said protecting member and electrically connected to said electrical conducting means, and the other of said first and said second parts being attached to said supporting structural unit and electrically connected to at least one of said terminal board areas, said first and said second parts being aligned so as to interconnect electrically upon insertion of said supporting structural unit in said enclosure; a fan mounted to said supporting structural unit, said fan being removable with said supporting structural unit and being electrically connected to the electrical terminal connection points of at least one of said terminal board areas; and means for manually varying the rating of said heater electrically connected to said heating means along said terminal board areas, said rating varying means comprising a plurality of jumper wires connected to preselected ones of said electrical terminal connection points, individual ones of said jumper wire plurality being rearranged manually to provide rating variation for said heater.
 8. The heater of claim 7 wherein said heating means comprises four heating elements, and said electrical connection means comprises a plug having a first male part and a second female part, one of said male and said female parts being mounted in the opening of said protecting member and electrically connected to said electrical conducting means, and the other said male and said female parts being attached to said supporting structural unit and electrically connected to said terminal board areas.
 9. The heater of claim 8 wherein said first electrical terminal board area of said supporting structure includes a first connection point, a second connection point, a third connection point and a fourth connection point, said second electrical terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, two and six, three and seven, and four and eight; said heater being adapted for 120 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of electrical connecting lines, one of said pair of connecting lines being electrically connected from said plug to said third connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removably connected along said first and said second terminal board areas for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first jumper wire connected between said first and said second connection points, a second jumper wire connected between said second and said fourth connection points, a third jumper wire connected between said third and said fourth connection points; said second terminal board area having a fourth jumper wire connected between said fifth and said sixth connection points, a fifth jumper wire connected between said sixtH and said eighth connection points and a sixth jumper wire connected between said seventh and said eighth connection points.
 10. The heater of claim 8 wherein said first terminal board area of said unit includes a first connection point, a second connection point, a third connection point, and a fourth connection point; and said second terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, points two and six, points three and seven, and points four and eight; said heater being adapted for 240/208 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of connecting lines, one of said pair of connecting lines being electrically connected from said plug to said sixth connection point, and the other of said pair of connecting lines being electrically connected from said plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removably connected along said first and said second terminal board area for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first wire electrically connected between said first and said second connection points, a second wire electrically connected between said second and said fourth connection points, and a third wire electrically connected between said third and said fourth connection points; and said second terminal board area of said supporting structure having a fourth wire electrically connected between said fifth and said sixth connection points, and a fifth wire electrically connected between said seventh and said eighth connection points.
 11. A heater comprising: an enclosure defining a chamber including a bottom wall, a top wall, and at least one sidewall, said top wall being pervious to air flow to and from said chamber, said sidewall having at least one opening in it; a protecting member mounted to said enclosure bottom wall and defining a raceway therewith, said opening in said sidewall communicating with said raceway; a supporting structural unit removably mounted within said chamber, said unit including a first electrical terminal board area, said first electrical terminal board area comprising a structure for attaching a first end of a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means; a second terminal board area spaced from said first electrical terminal board area, said second electrical terminal board area comprising a structure for attaching a second end of a heating means to said supporting structural unit, and a plurality of electrical terminal connection points for permitting the completion of electrical connections to said heating means; heating means including a plurality of heating elements attached to said supporting structural unit, each of said heating elements having a first end and a second end, said heating elements being attached to the terminal board areas of said supporting structural unit along said first and said second ends, the attachment of said heating means to said terminal board areas enabling said heating means to be removed from said chamber with said supporting structural unit, said first and said second ends of said heating elements being electrically connected to predetermined ones of said electrical terminal connection points; electrical conducting means in said enclosure and at least partially carried by said raceway, said electrical conducting means including meanS for electrically connecting said first and said second terminal board area to a source of electrical power; and means for manually varying the rating of said heater for a given input voltage electrically connected to said heating means along said terminal board area, said rating varying means comprising a plurality of jumper wires connected to preselected ones of said electrical terminal connection points, individual ones of said jumper wire plurality being rearranged manually to provide rating variation for said heater.
 12. The heater of claim 11 wherein said protecting member has an opening in it, said heater being further characterized by electrical connection means interposed in said electrical conducting means, said connection means including a first part and a second part electrically interconnectable with one another, one of said first and said second parts being mounted in the opening of said protecting member and electrically connectable to the source of electrical power through said conducting means, and the other of said first and said second parts being attached to said supporting structural unit and electrically connected to said first and second terminal board areas through said conducting means, said first and said second part being aligned for electrical interconnection upon insertion of said supporting structural unit in said enclosure.
 13. The heater of claim 12 further characterized by a fan mounted to said supporting structural unit, removable therewith and electrically connected to at least one of said first and said second terminal board areas.
 14. The heater of claim 13 wherein said heating means comprises four heating elements and said electrical connecting means comprises a plug having a first male part and a second female part.
 15. The heater of claim 14 wherein said first electrical terminal board area of said supporting structure includes a first connection point, a second connection point, a third connection point and a fourth connection point, said second electrical terminal board area of said supporting structure includes a fifth connection point, a sixth connection point, a seventh connection point, and an eighth connection point, one each of said four heating elements being electrically connected between said connection points one and five, two and six, three and seven, and four and eight; said heater being adapted for 120 volt operation, said fan being further characterized by an electrical motor mounted to said unit having a fan blade mechanically connected to it, said motor being electrically connected between said third and said seventh connection points, said plug including a pair of electrical connecting lines, one of said pairs of connecting lines being electrically connected from said plug to said third connection point, and the other of said pairs of connecting lines being electrically connected from said plug to said seventh connection point; said rating varying means comprising a plurality of jumper wires removably connected along said first and said second terminal board areas for varying the electrical interconnection of said four heating elements and said electrical motor, said first terminal board area having a first jumper wire connected between said first and said second connection points, a second jumper wire connected between said second and said fourth connection points, a third jumper wire connected between said third and said fourth connection points; said second terminal board area having a fourth jumper wire connected between said fifth and said sixth connection points, a fifth jumper wire connected between said sixth and said eighth connection points and a sixth jumper wire connected between said seventh and said eighth connection points. 